Automatic brake for power tools



March 19, 1957 J, ow JR 2;785,7l0

AUTOMATIC BRAKE FOR POWER TOOLS Filed may 3. 1954 fawn/vs TOOL ENTOR INV F|G.i JESSE R. MOWERY,JR.

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United States Patent 7 2,785,710 7 AUTOMATIC BRAKE FOR POWER TOOLS Jesse R. Mowery, In, Lancaster, Pa., assignor to De Walt Inc., a corporation of Pennsylvania Application May 3, 1954, Serial No. 427,22i

Claims. (Cl. 143-157) This invention relates to an improved brake for a power saw, particularly a circular power saw.

In many circular power sa-ws, the saw is mounted directly on the motor arbor and operates at a relatively high R. P. M. When the power is turned off, the motor and saw continue to coast, presenting a safety hazard since an operator is apt to be careless when the power is oil". Furthermore, there is a time loss where one must Wait for the blade to stop before making adjustments.

It has accordingly long been recognized that brake means should be provided so that motor and blade may be stopped simultaneously with turning off the power. Accordingly, it is my invention to provide an automatic braking means engaging the circular blade itself.

It is another object of my invention to apply a brake to the blade itself to prevent throw off.

It is a further object of my invention that the brake is always applied when the power is off.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation may be understood by reference to the apparatus embodying my invention and shown in the accompanying drawing in which 1 illustrate a side elevation, partly, in section, of a power driven rotary tool in conjunction with an automatic braking device.

With reference to the drawing, 1 show a motor 1% driving a rotating shaft 12 supporting a woodworking tool such as a saw blade 14 secured thereon. The saw blade guard 16 is secured to the motor by fastening means 18. The guard 16 has the oppositely facing bores 26 formed in its side walls 22. The flange cylinders 24 are secured in bores 20. These cylinders 24 are adapted to hold the spring-loaded pistons 26 which are urged by the compression springs 28 toward the blade or tool 14. A piston shaft 3% protrudes through and slidingly engages a bore 32 formed in the head of each cylinder 24.

There is secured to the bight 4d of guard 16 a doubleacting solenoid or electromagnet 42 having armature plungers 44. When solenoid 42 is activated, the plungers 44 retract longitudinally toward each other into the solenoid. A lever 34 pivotally fulcrumed on lugs 36 secured to guard 16 connects the ends of plungers 44 to the outw wardly extending ends of piston shafts 39.

In operation, the solenoid 42 is connected across the terminals 11 of motor 14 so as to be energized when switch 13, connected in series between power lines and motor 19, is closed so as to cause operating current to pass through the motor windings (Fig. 2). When so energized the armature shaft-s 44 are moved toward each other, rocking the lever 34 to move pistons 26 and brake shoes 27 against the thrust of compression springs 28 and away from the tool 14.

When, on the other hand, the power is turned oif, the solenoid 42 is de-energized and the springs 28 thrust pistons 26 and brake shoes 27 against the sides of tool 14 with braking force. By applying the brake to the blade itself I prevent a possible throw off which might occur where a braking force is applied to the motor 10 or motor shaft 12 itself.

Having described a working embodiment of my invention, I claim:

1. In combination with a power-driven rotary cutting tool having an electric motor and cutting tool mounted on the armature shaft of said motor, a guard mounted on said motor and about a portion of said cutting tool, said guard having a cylinder positioned longitudinally parallel to the armature of said motor, a piston movable to and fro in said cylinder, a brake shoe secured on one end of said piston to engage said rotary cutting tool when said piston is moved to the forward end of said cylinder, resilient means to urge said piston to said forward end of said cylinder and into braking contact with said rotary tool, a solenoid mounted on said guard, a fulcrumed lever connecting said solenoid to said piston, said solenoid and said lever being operatively positioned to move said piston against said resilient member and out of braking position when said solenoid is energized and means connecting said solenoid across the terminals of said electric motor to energize said solenoid when said motor is energized whereby said braking means may be moved by said resilient means into braking position when said motor is de-energized and said braking means may be moved out of braking position when said motor is energized.

2. In a cutting mach ne having a motor and a rotary cutting tool, a bracket mounted about the edge of said cutting tool, a pair of oppositely positioned members mounted on said bracket movable to effect equal frictional engagement simultaneously on opposite sides of said cutting tool, resilient means on each of said members operative to move said members into frictional engagement with said cutting tool, a double acting solenoid positioned on said bracket beyond said tool and intermediate said members, and a pair of fulcrumed levers pivoted to said bracket and each engaged at its one end to one end of said double acting solenoid and at its other end to one of said movable members to move said members against said yielding means and out of frictional engagement with said cutting tool.

3. in a cutting machine having a motor and a rotary cutting tool, a bracket mounted about the edge of said cutting tool, a pair of oppositely positioned members mounted on said bracket movable to effect equal frictional engagement simultaneously on opposite sides of said cutting tool, resilient means on each of said members operative to move said members into frictional engagement with said cutting tool, a double acting solenoid positioned on said bracket beyond said tool and intermediate said members, a pair of fulcrumed levers pivoted to said bracket and each engaged at its one end to one end of said double acting solenoid and at its other end to one of said movable members to move said members against said yielding means and out of frictional engagement with said cutting tool, and an electrical conductor operatively connected to said solenoid and to said motor to energize said solenoid when said motor is in operation.

4. in a cutting machine having an electric motor and a rotary cutting tool, a bracket mounted about the edge or" said cutting tool, a pair of oppositely positioned members mounted on said bracket movable to effect equal frictional engagement simultaneously on opposite sides of said cutting tool, resilient means on each of said members operative to move said members into frictional engagement with said cutting tool, a double acting solenoid positioned on said bracket beyond said tool and intermediate said members, a pair of fulcrumed levers pivoted to said bracket and each engaged at its one end to one 5. The combination with a power driven rotary cutting tool having an electric motor and a source of elec:

tnic power, a guardmounted about a portion of said rotary tool, a brake shoe mounted on said guard on each side .of said tool movable from a tool engaging position to a non-engaging position, means to move said brake shoes into tool engaging position, a single electro-magnetic means to move said brake shoes out of tool engaging position, and single switch means operative when plosed to pant es; said, motor and said eleetrotnagnetic means to said source of power whereby said brake shoes are uniformly moved out of engaging position during the operation of said motor and uniformly released into braking position when said switch means is opened to stop said motor.

References Cited the tile of this patent UNITED STATES PATENTS 1,282,483 Steen Oct. 22, 1918 1,811,066 Tannewitz a y a June 23, 193 1 FQREIGN PATENTS 485,143 Germany Nov. 27, 1929 

